Liquid molded hollow cell core composite articles

ABSTRACT

A hollow core composite assembly  10  is provided, including a hollow core base  12  having an open core surface  14 , a polyetherketoneketone film  22  applied to the hollow core base  12 , and an adhesive layer  24  positioned between the polyetherketoneketone film  22  and the open core surface  14 . The resultant hollow core composite assembly  10  can be cured to provide a structure suitable for use within a liquid molding process.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is one of two related applications being filed on the sameday. The second is entitled Liquid Molded Hollow Cell Core CompositeArticles filed on Oct. 30, 2001, Ser. No.______(01-194/009873 BOE 0279PA).

TECHNICAL FIELD

[0002] The present invention relates generally to hollow cell corecomposite articles and more particularly to a liquid molded honeycombcore composite articles.

BACKGROUND OF THE INVENTION

[0003] The cornerstone of aeronautics, avionics, and spacecraft designhas been the ability to design lightweight components that maintainstructural strength and integrity. These characteristics play a crucialrole not only in traditional design considerations such as flightcapabilities and structural integrity, but also play a crucial role inthe adaptability and commercial performance of a given craft design.Reduced weight and structural fortitude can play a significant role infuel consumption, craft profile, and cargo and/or passenger capacity.The increase in profitability associated with the aforementionedfactors, as well as a variety of others, has provided strong motivationfor design advancements in the area of strength/weight improvement.

[0004] A significant advancement in the development of low weight/highstrength structures was the development of the hollow cell cores, suchas honeycomb cores. Hollow cell cores provide a high strength structuralbase while minimizing the negative effects of the weight associated withthe core material by containing voids within the core material thatprovide for significant weight savings as compared to a solid component.The high strength/low weight characteristic of hollow cell cores hastherefore resulted in the popularity of their use within the aeronauticsindustry as well as a variety of other industries.

[0005] Despite the popularity of hollow cell core materials, such ashoneycomb cores, there use has not been suitable for certainmanufacturing processes. Liquid molding processes, for example, canpresent problems when applied to hollow cell core materials. Liquidmolding composite manufacturing processes, such as resin transfermolding, vacuum assisted resin infusion, vacuum infusion molding, andothers, present fundamental concerns for the use of hollow cell corematerials. When these processes are used, it is possible for the hollowcells to fill with liquid resin prior to curing. This can make theresulting structure resin rich, heavy, and generally undesirable. Itwould be highly desirable to have the ability to apply liquid moldingapproaches to hollow cell core materials without the concerns forcompromised cells.

[0006] Numerous approaches have been developed in an attempt to solvethe hollow cell core/liquid molding dilemma. Often, however, theresulting solutions add undesirable weight and/or production costs tothe resulting hollow core composite articles. One solution pre-processesthe core to seal the cells with film adhesive, or film adhesive andprepreg, prior to liquid molding composite article fabrication toprevent liquid molding resin from penetrating the cells. Other processesinclude filling the hollow cells, for example, with a closed cell foamor material. This, however, often adds undesirable weight to theresulting article. Precured composite sheets autoclaved to the hollowcell core add additional weight and require a costly autoclavingprocess. Although a variety of other attempts are known to seal thehollow cell core, often these attempts result in undesirable weightincreases, increases in the number of processing steps, and undesirablecost increases.

[0007] It would, therefore, be highly desirable to have a method forsealing hollow cell core material such that the hollow cell corematerial may be successfully used with known liquid molding approacheswithout penetration of the hollow cells by the liquid molding. Inaddition, it would be highly desirable for such a protective hollow cellcore material to withstand liquid molding approaches without undesirableincreases in weight or the requirement for costly manufacturingprocesses.

SUMMARY OF THE INVENTION

[0008] It is, therefore, an object of the present invention to provide aliquid molded hollow core composite assembly for use in low weight/highstrength articles. It is a further object of the present invention toprovide a liquid molded hollow core composite assembly that can bemanufactured without resulting in undesirable increases in compositeassembly weight or manufacturing time and cost.

[0009] In accordance with those and other objects of the presentinvention, a hollow core composite assembly is provided. The hollow corecomposite assembly includes a hollow core base having at least one opencore surface. The hollow core composite assembly further includes apolyetherketoneketone film applied to the open core surface. At leastone adhesive film is positioned between the open core surface and thepolyetherketoneketone film to bond the surfaces together. The resultanthollow core composite assembly is then suitable for use in liquidmolding processes such as resin transfer molding or resin infusionprocesses.

[0010] Other objects and features of the present invention will becomeapparent when viewed in light of the detailed description of thepreferred embodiment when taken in conjunction with the attacheddrawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is an exploded view illustration of an embodiment of ahollow core composite assembly in accordance with the present invention;

[0012]FIG. 2 is an exploded view of an alternate embodiment of a hollowcore composite assembly in accordance with the present invention;

[0013]FIG. 3 is an exploded view of an alternate embodiment of a hollowcore composite assembly in accordance with the present invention; and

[0014]FIG. 4 is a flow-chart illustration of a method of producing ahollow core composite assembly in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0015] Referring now to FIG. 1, which is an illustration of anembodiment of a hollow core composite assembly 10 in accordance with thepresent invention. The hollow core composite assembly 10 is intended foruse within the aeronautics and spacecraft industry, although it iscontemplated that the present invention may be utilized within a widevariety of fields. The hollow core composite assembly 10 provides alightweight and cost effective method of providing structural assembliesfor use in aircraft and spacecraft design.

[0016] The hollow core composite assembly 10 includes a hollow core base12 A wide variety of hollow core base 12 embodiments are known withinthe prior art. One such embodiment is a honeycomb core. The advantage ofhollow core bases 12 is that they provide a low weight/high strengthstructure popular within the aeronautics field. A traditionaldisadvantage to such hollow core bases 12 is that they commonly containat least one open core surface 14 where the hollow cores 16 are exposed.This open core surface 14 provides access to the hollow cores 16 and canprovide a mechanism for liquid resin from the resin transfer moldingprocess or vacuum assisted resin transfer molding process, to penetratethe hollow core base 12 and thereby suffer losses to its weightbenefits. Although it is possible for a hollow core base 12 to have asingle open core surface 14, commonly a hollow core base 12 will have anupper open core surface 18 and a lower open core surface 20.

[0017] The present invention seals and protects the open core surfaces14 through the use of a bondable solid film 22 applied to the open coressurfaces 14. A variety of bondable solid films 22 are contemplated bythe present invention. One embodiment contemplates the use of apolysulphone (PSU) film. Other embodiments include, but are not limitedto, bondable solid films 22 such as forms of, polyethyleneterephthalate(PET), nylon, thermoplastic polymer materials, metal foils, thermosetfilm materials, and urethane film materials. The primary characteristicof the solid bondable film 22 is to be impervious to penetration of theliquid resin of choice in the composite liquid molding process (such asvinyl ester, polyester epoxies, phenolids, cynate esters, etc.) andbondable to the hollow core base 12 with or without the addition of anadhesive. The solid bondable film 22 provides a barrier to preventsubsequent liquid molding materials from penetrating the hollow cores 16and thereby compromising the integrity of the hollow core compositeassembly 10.

[0018] One novel embodiment contemplates the use ofpolyetherketoneketone (PEKK) as the solid bondable film 22. The use ofPEKK provides a variety of advantages over many films when the hollowcore composite assembly 10 is for use in unique applications. Oneadvantage, is that the PEKK film has a relatively low dielectricconstant. This can be an important factor when the hollow core compositeassembly 10 is intended for use within low observable aircraft. The lowdielectric constant can be advantageous to designs wherein low radarprofile or radar invisibility is desired. The use of PEKK also providesthe advantage of providing a solid bondable film 22 with improvedbonding characteristics over many solid films. This can improve andsimplify the manufacturing process as well as improve the integrity ofthe resulting composite. Although the PEKK film 22 may be formed in avariety of dimensions, one embodiment contemplates the use of a 1.1millimeter film.

[0019] The hollow core composite assembly 10 can further include anadhesive layer 24 positioned between the solid bondable film 22 and theopen core surface 14. The adhesive layer 24, such as an adhesive film,can be utilized to assist the bonding of the solid bondable film 22 tothe hollow core base 12. Although a variety of adhesive layers 24 arecontemplated, one embodiment contemplates the use of FM300 filmadhesive. Other contemplated adhesives 24 include, but are not limitedto, thermoplastic adhesive, hot melt adhesive, epoxy paste, BMI paste,and cyanate ester paste adhesives. It is envisioned that the solidbondable film 22 and the adhesive layer 24 are attached to the hollowcore composite assembly 10 as part of the composite article perform. Thethermal cycle to enhance the bonding characteristic of the solidbondable film 22 to the open core surface 14 (with or without thepresence of the adhesive layer 24) can be included in the singleprocessing cycle for the hollow core composite assembly 10 and therebylower processing costs and cycle time. It should be understood, however,that the solid bondable film 22 may be bonded to the hollow core base 12prior to the composite article processing cycle as a separate processingstep such as pre-curing. Pre-curing refers to curing the chemicallyactive, material of a detail/subassembly prior to a future cure of amore complete assembly. In one embodiment of the present invention, thehollow core base 12 and bondable solid film 22 can be “pre-cured” priorto a liquid molding operation. During a liquid molding operation theinjectioned or infused resin would then be cured.

[0020] In an alternate novel embodiment, illustrated in FIG. 2, thepresent invention can further include at least one outer adhesive film26 applied to the outer surface 28 of the solid bondable film 22. Adistinct and novel aspect of this embodiment, is that it can assist inimproving the bondable outer surface 28 of the solid bondable film 22 inorder to ensure an improved hollow core composite assembly 10 whensubjected to liquid molding techniques. Prior processes often requiredspecialized surface preparation or coatings to insure that the liquidmolding techniques securely bonded to the hollow core composite assembly10. These specialized preparations could undesirably increase the cost,process steps, and time of manufacture. The present embodiment providesa relatively quick and efficient way of improving the bondable outersurface 28 of the solid bondable film 22 without the need for expensiveand time consuming processes. It may also serve to increase the range ofsolid bondable films 22 available for a given application.

[0021] Referring now to FIG. 3, the present invention can furtherinclude at least one dry face ply 30 laid up dry and placed on top ofthe solid bondable film 22. Although a single dry face ply 30 can beused, it is contemplated that a plurality of dry face plies 30 are to beused to result in a composite sandwich panel of face skins. The face ply30 (reinforcing ply, reinforcement, etc.) of the resulting compositearticle may consist of carbon fiber, fiberglass, Spectra, Kevlar fabricor other high performance reinforcement material. Although a single dryface ply 30 can be used, it is contemplated that low resin content ortackified ply could be used. This type of reinforcement material andstyle of reinforcement form (weave, mat, yarn or tow) is dependent onthe design and function of the resulting composite article and may beinfinitely tailored to meet the desired need. A wide variety of dry faceplies 30 are well known in the industry and can be used in combinationto provide structural surfaces with unique properties. One advantage ofusing a plurality of dry face plies 30 is that the hollow core compositeassembly 10 can be quickly and simply assembled and a single liquidmolding process and all of the subsequent thermal processing, bondingsteps and resin infusion can be performed simultaneously. This providessignificant production cost and time advantages over many prior artmethods.

[0022] Finally, liquid resin 32 is applied to the dry face ply 30, orplies, and the hollow core composite assembly 10 is cured. The liquidresin 32 wets out the dry plies 30. A single liquid resin 32 may beapplied, or a plurality of liquid resins 32 may be utilized. Once cured,the resulting assembly 10 becomes a sandwich panel of face skinssurrounding a hollow core base 12. The liquid resin 32 is contemplatedto be applied in any of a variety of known fashions. In one embodiment,it is contemplated that the liquid resin 32 is applied using a resintransfer molding process. In alternate embodiments, however, the liquidresin 32 can be applied using a variety of processes including, but notlimited to, vacuum assisted resin transfer molding, vacuum infusionmolding processes, etc. The liquid resin 32 may be applied to thecomposite article in a variety of means such as wet lay-up, resintransfer molding processes, SCRIMP, vacuum assisted resin transfermolding processes, vacuum infusion molding processes, etc. For each ofthe named processes, the liquid molding resin 32 is selected based onthe process method, composite article end item requirements, compositearticle use and other factors. After the application of the liquid resin32, the resin is allowed to set (or cure) to a rigid form permitting thecomposite article to be removed from the tool or mold. The method ofcure is dependent upon the selected liquid resin 32. Many types ofpolyester resin commonly used in the marine industry cure at ambienttemperatures (70 deg F.) in a given amount of time, while many aerospacegrade structural epoxy resins cure at 350 deg F. Each type of resin hasvarying cure requirements. After removal of the composite article fromthe tool or mold, it may undergo a post cure to enhance the resinproperties or the composite article.

[0023] Referring now to FIG. 4, which is an embodiment of a method ofproducing a hollow core composite assembly in accordance with thepresent invention. The method includes applying an adhesive film to anopen core surface of a hollow core base 100. The method further includesapplying a polyetherketoneketone film to the open core surface 102. Inan alternate embodiment, adhesive film may be applied directly to thepolyetherketoneketone film and then applied to the open core surface.The method can optionally further include applying an outer adhesivefilm to the outer surface of the polyetherketoneketone film 104. In oneembodiment, the method can include precuring the adhesive films andpolyetherketoneketone film to the hollow core base 106. In otherembodiments, however, the adhesive films and polyetherketoneketone filmsmay be cured to the hollow core base as part of a resin applicationprocess. A liquid resin can then applied to the hollow core compositeassembly 108. This may be accomplished in a single liquid resinapplication or may include a plurality of liquid resin applications. Inaddition, it is contemplated that the liquid resin may be applied in avariety of fashions including, but not limited to resin transfer moldingand vacuum infusion molding processes. Finally, the hollow corecomposite assembly is cured 110. A variety of curing processes arecontemplated by the present invention and may be used alone or incombination to effectuate curing base upon the curing requirements ofthe liquid resin, the adhesive film, and the hollow core base.

[0024] While particular embodiments of the invention have been shown anddescribed, numerous variations and alternative embodiments will occur tothose skilled in the art. Accordingly, it is intended that the inventionbe limited only in terms of the appended claims.

What is claimed is:
 1. A hollow core composite assembly, comprising: ahollow core base including at least one open core surface; at least onepolyetherketoneketone film affixed to said at least one open coresurface; and at least one adhesive layer positioned between said atleast one open core surface and said at least one polyetherketoneketonefilm.
 2. A hollow core composite assembly as described in claim 1,wherein said at least one adhesive layer is an uncured adhesive film. 3.A hollow core composite assembly as described in claim 1, wherein saidat least one polyetherketoneketone film and said at least one adhesivelayer are bonded to said hollow core base using a pre-cure process.
 4. Ahollow core composite assembly as described in claim 1, wherein said atleast one polyetherketoneketone film and said at least one adhesivelayer are bonded to said hollow core base by curing as part of a resinapplication process.
 5. A hollow core composite assembly as described inclaim 1, further comprising: at least one outer adhesive film applied toan outer surface of said at least one polyetherketoneketone film.
 6. Ahollow core composite assembly as described in claim 1, wherein said atleast one adhesive layer is an epoxy paste adhesive.
 7. A hollow corecomposite assembly as described in claim 1, wherein said at least oneadhesive layer is cyanate ester paste adhesive.
 8. A hollow corecomposite assembly as described in claim 1, wherein said at least oneadhesive layer is thermoset adhesive.
 9. A hollow core compositeassembly as described in claim 1, wherein said at least one adhesivelayer is a thermoplastic adhesive.
 10. A hollow core composite assemblyas described in claim 1, wherein said hollow core base is a honeycombcore.
 11. A hollow core composite assembly as described in claim 1,further comprising: a liquid resin applied using a liquid moldingprocess, said liquid resin applied over the hollow core base after saidat last one adhesive layer and said at least one polyetherketoneketonefilm are applied to said hollow core base.
 12. A hollow core compositeassembly, comprising: a hollow core base including at least one opencore surface; a solid film affixed to said at least one open coresurface; at least one adhesive layer positioned between said at leastone open core surface and said solid film; and at least one outeradhesive film applied to an outer surface of said solid film.
 13. Ahollow core composite assembly as described in claim 12, wherein said atleast one adhesive layer is an uncured adhesive film.
 14. A hollow corecomposite assembly as described in claim 12, wherein said at least onesolid film is a polyetherketoneketone film.
 15. A hollow core compositeassembly as described in claim 12, wherein said solid film and said atleast one adhesive layer are bonded to said hollow core base by curingas part of a resin application process.
 16. A hollow core compositeassembly as described in claim 12, wherein said at least one adhesivelayer is an epoxy paste adhesive.
 17. A hollow core composite assemblyas described in claim 12, wherein said at least one adhesive layer is acyanate ester paste adhesive.
 18. A hollow core composite assembly asdescribed in claim 12, wherein said at least one adhesive layer is a hotmelt adhesive.
 19. A hollow core composite assembly as described inclaim 12, wherein said at least one adhesive layer is a thermoplasticadhesive.
 20. A hollow core composite assembly as described in claim 12,wherein said at least one adhesive layer is a BMI paste adhesive.
 21. Ahollow core composite assembly as described in claim 12, wherein said atleast one outer adhesive film is an epoxy paste adhesive.
 22. A hollowcore composite assembly as described in claim 12 wherein said hollowcore base is a honeycomb core.
 23. A hollow core composite assembly asdescribed in claim 12 wherein said hollow core base is an open cellfoam.
 24. A hollow core composite assembly as described in claim 12further comprising: a liquid resin applied using a liquid moldingprocess over the hollow core base after said at least one adhesivelayer, said solid film, and said at least one outer adhesive film areapplied to said hollow core base.
 25. A method of sealing a hollow corebase for use in a liquid molding application process, comprising:applying an uncured adhesive layer onto an open core surface of thehollow core base; and applying a polyetherketoneketone film onto saidopen core surface.
 26. A method of sealing a hollow core base for use ina liquid molding application process as described in claim 25, furthercomprising: applying an outer adhesive film to an outer side of saidpolyetherkeytonkeytone film.
 27. A method of sealing a hollow core basefor use in a liquid molding application process as described in claim25, further comprising: pre-curing said uncured adhesive layer and saidpolyetherketoneketone film to the hollow core base.
 28. A method ofsealing a hollow core base for use in a liquid molding applicationprocess as described in claim 25, further comprising: curing saiduncured adhesive layer and said polyetherketoneketone film to the hollowcore base as part of the liquid molding application process.